During the 1980s the Oregon Institute of Science and Medicine developed food storage recommendations that were subsequently adopted and publicized by FEMA.
The food storage suggestions are as follows:

1. Store whole grain - not ground or otherwise processed - corn, wheat, and soybeans in a ratio by weight of 2:2:1. In other words, if one is storing 40 pound plastic, nitrogen-packed pails of grain, store 2 pails each of wheat and corn for each single pail of soybeans. Combined in these proportions, ground to flour, cooked (as in corn bread), and eaten, 2 to 3 pounds per day of this mixture will provide the nutrition required for a marine in combat - except for vitamin C and salt. An ordinary person surviving during an emergency would require perhaps half as much. Note: soybeans must be cooked before eating to avoid danger to health.

Nitrogen packing helps to assure that insects cannot infest the food. Containers should be long-lived and rodent resistant. There are several good commercial sources of food already appropriately packaged for storage - for example, Walton Feed in Idaho.

2. Store 1 kilogram of ascorbic acid (vitamin C) for each person-year of food. This is 3 grams per day. People under stress require extra vitamin C for optimum health. For prevention of death from scurvy, however, about 1% of this amount will suffice, so storage of vitamin C in these amounts might save the lives of an entire community.

Store CRYSTALLINE vitamin C - not pills. During storage, the pills may deteriorate. In a cool, dry bottle, crystalline vitamin C will last indefinitely. Vitamin C can also be obtained by simply sprouting some of the food grain before eating. In a serious emergency, however, sprouting may prove difficult. Store also, in a cool place, a supply of ordinary multivitamin pills.

3. Store lots of salt. This could be crucial to saving many lives. An inexpensive and convenient form is in bags or salt blocks obtained from a local farm feed store.

4. For infants, store dried milk available from food storage suppliers in cans. Infants can live on the grain ration, but they may refuse to eat less familiar food and will do better with milk.

5. Store several 20 litre (5 gallon) plastic buckets each containing 25 pounds of ordinary table sugar - sucrose; 1 pound baking soda; 5 x 11 ounce containers of Lite salt - KCl &NaCl; and a teaspoon for measuring. Dehydration from burns and diseases such as cholera can be treated with proper oral administration of these items. Instructions can be found in the March 1988, Volume 1, # 12, Fighting Chance newsletter. These buckets could save many lives during a serious prolonged emergency, where ordinary medical care is not available.

In ordinary times, soy bean, corn, and wheat flour can serve as a base for delicious and nutritious corn bread - when cooked with lots of baking soda, vegetable oil, and fruit for flavor.

It is best to store food now, while it is still available at a reasonable price.

The DFSP gives you a solid place to start your food storage program, keeps you organized and on track. If you already have a food pantry, it will point out what areas are deficient toward your chosen goal and what areas are already ship-shape. It has a reminder column for when you need to rotate food so nothing ever goes to waste. The DFSP can keep track of non-food items, too, like medicines and hygiene, plus cleaners and household items. You can even plan for your pets.

Simply fill in the number of family members for each age group and how many weeks you want to plan for and the spreadsheet calculates the rest. Easy-to-following instructions for how to use the DSFP are embedded into the spreadsheet so they can't 'go missing'."

There is a Latter Day Saint preparedness manual at this link. It is a compilation of many authors articles in their area of expertise. A great deal of material on the gathering, storage, and preparation of food. I runs the gamut of just about all a family would need to prevail in a long term crisis. Glean What you will.

Please consider sending them $10.00 if you wish to have this in hard copy, or as a courtesy for the pdf. It is really set up fpr the members of this church.

Is storing silica gel with packets of seeds that haven't been opened (in an air tight glass jar) safe / healthy?

According to sources that i have come across, yes it is ok, just make sure the actual crystals don't come into contact with the seed.
The crystals absorb any additional moisture from the surrounding air where they are used.

I use an evacuated heat sealed plastic bag as the excess air is withdrawn, and no insects or insect eggs that may hatch can survive as their is no oxygen for them to live in.